Wars over the Baltic

Several European powers regarded the Baltic Sea as of vital importance.[6] It served as a source of important materials and as a growing market for many commodities.[6] So large did the importance of the region loom that it became of interest even to powers that did not have direct access to it, such as Austria and France.[6] For several centuries, Sweden and Denmark would attempt to gain total control of the sea, a policy which other local and international powers opposed.[3][6] Historians have described the control of the Baltic as one of the main goals of Denmark's and Sweden's policies.[7][8][9][10]

The Scandinavian (Nordic) powers, who sensed opportunity in the power vacuum created by the weak or non-existent naval power of the Holy Roman Empire and Poland–Lithuania, adopted expansionist policies which fostered conflict over the Baltic.[3][11]
Denmark and Sweden used their control of parts of the Baltic to fuel their militaries.[3] Each claimed the Baltic as their own, and promised to protect foreign shipping.[3] While the Nordic powers vied with one another over control, they both agreed that it should be the domain of one of them, not of an "outsider" like Poland or Russia.[5] The Scandinavian powers tried to prevent the rise of their opposition through diplomatic treaties, which forbade other powers like Russia or Germany to build navies, and through military actions, whether targeting opponent naval forces, or through taking control of the Baltic ports.[5] In one of the most notable actions to retain its monopoly over the Baltic, Denmark in 1637 destroyed, without declaration of war, the nascent Polish–Lithuanian Commonwealth Navy.[5]

The numerous wars fought for the dominium maris baltici are often collectively referred to as the Northern Wars.[12] Initially Denmark had the upper hand, but eventually it lost ground to Sweden.[13] Neither Denmark nor Sweden managed to realize thorough military and economic control of the Baltic, though Sweden during her time as an empire came closest to that aim before the Great Northern War of 1700–1721.[6]

Danish dominium maris baltici

Main trading routes of the Hanseatic League

Historiography uses the term dominium maris baltici either in a narrower sense as a new Swedish concept of the Early Modern era, closely tied to the Swedish Empire,[14] or in a wider sense including the preceding Danish hegemony in the southern Baltic Sea.[15]

Denmark had subdued the southern Baltic coast from Holstein to Pomerania in the 12th century, but lost control in the 13th century after her defeat by German and Hanse forces in the Battle of Bornhöved (1227), retaining just the principality of Rügen. Thereafter, the Hanseatic League became the dominant economic power in the Baltic Sea.[15] Robert Bohn credits Valdemar IV "Atterdag" of Denmark (reigned 1340–1375) as the first Danish king to pursue a policy of establishing a Danish dominium maris baltici, aiming at adding to Denmark's naval dominance an economical hegemony at the expense of the Hanseatic League.[15] To achieve this aim, Valdemar sold Danish Estonia to the Teutonic Order state in 1346, consolidating his finances and raising an army from the revenue.[15] After initial territorial gains, Valdemar conquered the Hanseatic town of Visby (Gotland) in 1361, resulting in a war decided in favour of the League in the peace of Stralsund in 1370, which marked the climax of Hanseatic power.[16]

Atterdag's daughter and de facto successor, Lady Margaret, managed to concentrate the crowns of Denmark, Norway and Sweden in her Copenhagen-centered Kalmar Union from 1397.[17] In 1429, Kalmar king Eric of Pomerania started to raise the Sound Dues from merchants entering or leaving the Baltic Sea, allowing the Copenhagen court to benefit from the Baltic Sea trade profits without engaging in economic adventures itself.[18] The Sound Dues, imposed until 1857 and constituting a primary source of income for the Royal treasury, quickly became a contentious issue, which brought Denmark into conflict with the Hanseatic League and the neighboring powers.[19]

Aftermath

The failure of the Scandinavian powers to take control of the Baltic, and steadfast refusal of other powers – local and international – to recognize their claims, is seen as one of the factors that led to the development of the "freedom of the seas" principle in international law.[6]